The present invention relates to compositions of matter that exhibit piezoelectric phenomena, and more specifically to such composites formed from conductive and/or semi-conductive materials and dielectric materials.
Piezoelectricity is an effect by which energy is converted between the mechanical and electrical forms. The general form of linear coupling between stress tensor σJ and polarization vector Pi in direct piezoelectric effect is given by the equationPi=diJσJ  (1)
where diJ is the piezoelectric charge constants and indexes i={1, 2, 3}, J={1, 2, . . . , 6}. For index J the Voigt notation conversion is used.
Consider a crystal of piezoelectric material 10 with an electrical axis in the z direction (FIG. 1). Mechanical compression or tension acting in parallel to the z axis on the crystal induces excess of charge densityΔq=P3=d33σ3  (2)
The conversion of mechanical forces into electric potential (charge excess) is known as direct piezoelectric effect. The inverse process of conversion of electric potential into mechanical motion is known as inverse piezoelectric effect.
Today, for micro and nano-electromechanical systems, PbZn1-xTixO3 wherein x is about 0.48 (PZT) is widely used in the form of thin films. However, PZT films, like other ceramic materials, are extremely brittle. Further, PZT thin films exhibit a hysteresis effect. In addition, the piezoelectric coupling constancies of PZT materials are strongly temperature dependant. The nonlinear effects, parameter variations, and other phenomena and effects observed in piezotransducers make it extremely difficult to integrate the piezotransducer dynamics. In fact, the steady-state analysis does not allow one to fully examine the system performance and make a conclusion based on requirements and specifications imposed.
It is therefore a first object of the present invention to provide piezoelectric materials for transducers, sensors and other applications that have a high piezoelectric coefficient yet are not brittle.
It is a further object of the invention to provide such piezoelectric materials in the form of thin films for ease of integration with micro electrical mechanical systems (MEMS) or nano-electrical mechanical systems (NEMS).